I am using akismet to check for comment spam, and it works. However, I would also like to stop them from registering in the first place.
Is there something I can use like akismet to check the registration details?
You could try making ip address validation, it could help you make every registration unique. While the form submit, you could check with the other registered users' ip address and restrict multiple registration of the spammers from the same id, as they(spammers) usually make multiple ids and probably from a same computer.
Useful source:
You should probably add some captcha to your registration form. Adding an anti cross site request forgery field also helps.